Fiber array ferrule and method of making

ABSTRACT

The array ferrule of the present invention has a main body having a fiber receiving cavity which extends therethrough from a mating face to a rear end. A pair of pin slots is formed in opposing side walls of the main body being precisely located with respect to the fiber receiving cavity. In communication with each pin slot is a retention member slot for receiving a pin retention member. A plurality of fibers is precisely positioned within the fiber receiving cavity and an encapsulant substantially surrounds the fibers to substantially fill the fiber receiving cavity. 
     A method of making the array ferrule begins with providing a ferrule blank having a pair of preformed slots extending inward from the opposing side walls. The blank is precisely aligned on a mandrel which is placed within the fiber receiving cavity. Pin slots are broached in each side surface in the area of the preformed slots to form the ferrule main body. The ferrule main body is then positioned within a ferrule receiving opening of a central fixture such that locating pins of the central fixture are positioned within the pin slots. The fiber receiving cavity is then populated with a plurality of optical fibers which are accurately located using a plurality of combs over the ends of the optical fibers which protrude from the mating face. Finally, the fiber receiving cavity is filled with an encapsulant.

FIELD OF THE INVENTION

The present invention relates to optical connectors and moreparticularly to an array ferrule and a method of making an array ferrulefor use in such optical connectors.

BACKGROUND OF THE INVENTION

Communication systems have grown in complexity furthering the need forgreater broadband capabilities. Optical communication systems have beenemployed in these communication systems and especially in broadbandsystems for meeting the need to transport large quantities of data,voice and other types of communications over a relatively compactnetwork. Miniaturization of components in optical communication networksalso continues to be necessary. Accordingly, multi fiber opticalconnectors such as the MT-RJ connector have become increasingly popularbecause of their ability to easily connect a plurality of fibersutilizing a standard form factor within the telecommunications industry.MT-RJ connectors have the capability of terminating a pair or a singlerow array of fibers utilizing a ferrule within the same connectorhousing that was previously used for a fiber pair termination.

One such connector has been developed by the MT-RJ Alliance includingthe companies of Hewlett-Packard, Fujikura, AMP, Siecor, and Usconec.The MT-RJ connector family utilizes an MT ferrule designed to hold 2, 4,8, 12 or 16 fibers in a linear array. The MT ferrule is a precisionmolded solid part having tapered fiber receiving passageways which areloaded with a ribbon fiber array from a rear end. In line with the fiberarray are a pair of pin receiving holes which are used to align theferrule end faces of two mated ferrules. The pin holes must be preciselylocated with respect to the array of fiber receiving channels in orderto insure proper alignment and to minimize optical signal attenuationbetween mated fiber end faces.

U.S. Patent Application Publication U.S. 2003/0016918 provides a multifiber optical ferrule having a group of fibers terminated from a ribbonand arranged in a linear array. The ribbon is secured into the ferrulewith epoxy introduced through a transverse window formed in the ferrule.Once the epoxy is cured, the fibers are cleaved and polished at thefront end or mating face to complete the ferrule and fiber arrayassembly. The ferrule and fiber array assembly may then be loaded into avariety of connector housings which are part of the MT-RJ or otherconnector systems. Although that publication provides for a multi fiberoptical ferrule having a group of fibers arranged in a linear array, itis desirable to increase the number of fibers which may be terminated bysuch an array ferrule. There is a need, however, to increase the densityof fibers in the array while maintaining the same MT-RJ form factor andhousing. It should be understood that this problem is not limited to theMT-RJ form factor, but that the need for high density extends to manyfiber optic connector families. What is needed is a ferrule and methodwhich is capable of increasing the density of fiber terminations withinan existing optical connector housing.

SUMMARY OF THE INVENTION

The invention provides an array ferrule for use in a fiber opticconnector. The array ferrule has a main body having a fiber receivingcavity which extends therethrough from a mating face to a rear end. Pinslots are formed in opposing side walls of the main body and areprecisely located with respect to the fiber receiving cavity. Incommunication with each pin slot is a retention member slot forreceiving a pin retention member. A plurality of fibers is preciselypositioned within the fiber receiving cavity and an encapsulantsubstantially surrounds the fibers to substantially fill the fiberreceiving cavity.

A method of making the array ferrule begins with providing a ferruleblank having a pair of preformed slots extending inward from theopposing side walls. The blank is precisely aligned on a mandrel whichis placed within the fiber receiving cavity. Pin slots are broached ineach side surface in the area of the preformed slots to form the ferrulemain body. The ferrule main body is then positioned within a ferrulereceiving opening of a central fixture such that locating pins of thecentral fixture are positioned within the pin slots. The fiber receivingcavity is then populated with a plurality of optical fibers which areaccurately located using a plurality of combs over the ends of theoptical fibers which protrude from the mating face. Finally, the fiberreceiving cavity is filled with an encapsulant which is cured.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example with reference tothe accompanying figures of which:

FIG. 1 is a perspective view of the array ferrule according to thepresent invention;

FIG. 2 is a perspective view of a ferrule blank positioned within abroach for broaching the pin slots;

FIG. 3 is a perspective view of a partially assembled array ferrule ofFIG. 1;

FIG. 4 is a perspective view of an assembly tool for assembling thearray ferrule of FIG. 1;

FIG. 5 is a cross sectional view taken along the line 5—5 of FIG. 4;

FIG. 6 is a partially exploded perspective view of the central portionof the tool shown in FIG. 4;

FIG. 7 is a top view of the central portion of the tool in FIG. 4 in thefirst step of a progression which accurately positions the fibers withinthe fiber receiving cavity of the ferrule;

FIG. 8 is a top view of the central portion of the tool in FIG. 4 in thesecond step of a progression which accurately positions the fiberswithin the fiber receiving cavity of the ferrule;

FIG. 9 is a top view of the central portion of the tool in FIG. 4 in thefinal step of a progression which accurately positions the fibers withinthe fiber receiving cavity of the ferrule;

FIG. 10 is a partial cross sectional view taken along the line 10—10 ofFIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

The optical array ferrule 10 will first be described generally withreference to FIG. 1. The major components of the array ferrule include amain body 12 which supports pins 44 within pin slots 18. Retentionmembers 46 serve to hold the pins 44 within the pin slots 18. Aplurality of optical fibers 40 are positioned within a fiber receivingcavity 22 by an encapsulant 26. The plurality of optical fibers 40terminate along a mating face 14. Each of these major components willnow be described in greater detail with reference to FIGS. 1 and 3.

Referring first to FIG. 3, the main body 12 will be described in greaterdetail. The main body 12 is formed of a molded or cast material whichexhibits dimensional stability suitable for temperature cycling of agiven application. Various metallic compounds, plastics or othercomposites a suitable for forming the main body 12. For example suitablematerials include but are not limited to: Z-2, Z-5, Z-7, AL-60 63 orAL-60 61. A mating face 14 is formed on one end of the main body 12 anda rear end 16 is located opposite the mating face 14. A flange 15 ispositioned near the rear end 16. A pair of opposing side surfaces 24extend from the mating face 14 to the flange 15. A fiber receivingcavity 22 extends through the main body 12 between the side surface 24from the mating face 14 back to the rear end 16. A pair of pin slots 18are formed in the opposing side surfaces 24 and extend from the matingface 14 to the flange 15. The pin slots 18 are formed and located inprecise relationship to the fiber receiving cavity 22. A retentionmember slot 20 extends rearward from the mating face 14 toward theflange 15 and is in communication with the pin slot 18.

A plurality of optical fibers 40 may be arranged either as a bundle ormay emanate from a group of ribbon fibers to form an array which islocated within the fiber receiving cavity 22 as shown in FIG. 1. Thebundle of optical fibers 40 is terminated within the encapsulant 26along the mating face 14 as will be described below. The mating face 14is thereafter processed by cleaving the optical fibers 40 and polishingthe mating face 14 by well known techniques as will be described below.

A method of making the array ferrule 10 will now be described in greaterdetail with reference to FIGS. 2-10. Referring first to FIG. 2, a blank11 of the array ferrule 10 is formed by either molding or casting. Itshould be noted here that the blank 11 is formed to have preformed slots17 extending inward from the opposing side surfaces 24. Each preformedslot 17 extends inward only to the respective retention member slot 20.The blank 11 is held by a holding device 56 and is slid over a mandrel50 such that the mandrel is received within the fiber receiving cavity22 from the mating face 14. The mandrel 50 is tapered to preciselyposition the blank 11. The mandrel 50 is mounted on a carrier 52 whichis slidable over rails 58 toward a pair of broaches 54 which areprecisely located with respect to the mandrel 50. As the carrier 52 isslid past the broaches 54, precise pin receiving slots 18 are cut fromthe preformed slots 17. The resulting array ferrule main body 12 has apair of pin receiving slots 18 precisely located with respect to thefiber receiving cavity 22. The main body 12 is now ready for furtherassembly to produce the completed array ferrule 10.

An assembly tool 30 will now be described in greater detail withreference to FIGS. 4-6. Referring first to FIGS. 4 and 5, a table 62 hasa central opening 69 passing between its major surfaces in a centralregion. A central fixture 32 is located over the central opening 69 andis mounted to the table 62 by suitable fasteners 68. The central fixture32 has a pair of locating pins 36 mounted within a ferrule receivingopening 34. Guide slots 70 are provided along a major surface and extendoutward from the central opening 69. Comb mounts 64 are positioned overand are movable within the guide slots 70. A comb holder 66 is mountedon the top of each comb mount 64. A respective comb 38 a, 38 b, 39 a, 39b is mounted to each comb holder 66 utilizing a suitable fastener. Thecomb mounts 64 are slidable toward and away the locating pins 36 suchthat the combs 38 a, 38 b, 39 a, 39 b slide along a top surface 35 ofthe central fixture 32. Guide projections 63 extend downward from thecomb mounts into the guide slots and are slidingly received therein inorder to allow the comb mounts 64 to move in a controlled linear motiontoward and away from the locating pins 36.

The combs 38 a, 38 b, 39 a, 39 b will now be described in greater detailwith reference to FIG. 6. The combs 38 a, 38 b, 39 a, 39 b are eachformed of a sheet material having a thickness which is preferably amultiple of the optical fiber diameter. For example, this multiple maybe five times or greater in order to accurately position the opticalfibers 40 to be orthogonal to the mating face 14 as will be describedbelow. The comb 38 a has a plurality of long teeth 43 extending towardsand slightly beyond an end 47 to form a fiber receiving area 48 having aplurality of spaces between the long teeth 43. The comb 38 b issimilarly formed of a sheet material and has a plurality of short teeth45 extending outward to a complementary end 49 which is profiled to matewith the end 47. The short teeth 45 interlock between the spaces formedby ends of the long teeth 43 which project beyond the end 47. The comb39 a is oriented orthogonal to the combs 38 a, 38 b and is similarlyformed of a sheet material and features a plurality of long teeth 43extending outward to form a similar fiber receiving area 48. A pair ofalignment tabs 41 also extend outward slightly beyond the free ends ofthe long teeth 43. Each alignment tab 41 has a semi-circular free end.The alignment tabs 41 extend outwardly from a respective referencesurface 51 formed along the outside of each alignment tab 41. The comb39 b is similarly formed of a sheet material and features a plurality ofshort teeth 45 being profiled to interlock in the space formed by thefree ends of the long teeth 43 on the comb 39 a. A pair of alignmentrecesses 42 are formed to be complementary to the semi-circular freeends of the alignment tabs 41. A second reference surface 53 is providedon the outside of each alignment recess 42.

In assembly, the formed main body 12 is placed within the ferrulereceiving opening 34 such that the locating pins 36 are positionedwithin the pin slots 18 in order to precisely locate the fiber receivingcavity 22 with respect to the combs 38 a, 38 b, 39 a, 39 b. The opticalfibers 40 are then positioned within the fiber receiving cavity 22 asbest shown in FIGS. 6 and 3.

Alignment of the optical fibers 40 within the fiber receiving cavity 22will be described in greater detail with reference to FIG. 6 and theprogression shown in FIGS. 7-9. Referring first to FIG. 7, once theoptical fibers 40 are roughly aligned within the fiber receiving cavity22, the combs 38 a and 38 b are moved in the direction shown by thearrows in FIG. 7 by sliding the comb mounts 64 within the guide slots 70such that the plurality of optical fibers 40 are aligned in between theinterlocking long and short teeth 43, 45. Next, as shown in FIG. 8, thethird and fourth combs 39 a and 39 b are moved towards each other in thedirection shown by the arrows in FIG. 8 such that the optical fibers 40are positioned between the interlocking long and short teeth 43, 45.Reference surfaces 51, 53 are positioned to engage the locating pins 36in order to precisely locate the optical fibers 40 with respect to thelocating pins 36 and the pin slots 18. Once the optical fibers 40 areprecisely positioned within the combs 38 a, 38 b, 39 a, 39 b as bestshown in FIG. 10, an encapsulant 26 is injected into the passageway 28(FIG. 1) through an encapsulant supply tube and allowed to cool in orderto fix the optical fibers 40 in precise location within the fiberreceiving cavity 22. A suitable encapsulant is a metallic material, forexample “Cerrocast”, available from several metal suppliers, such asCanada Metal. It should be understood that other encapsulants are withinthe scope of the invention and may be substituted for the metallicencapsulant. The array ferrule 10 is then removed from the ferrulereceiving opening 34. The optical fibers 40 are cleaved and the matingface 14 is polished by well known techniques in order to complete thearray ferrule 10.

The foregoing illustrates some of the possibilities for practicing theinvention. Many other embodiments are possible within the scope andspirit of the invention. For example, the methods of the invention maybe used to create various array configurations of fibers in rectangularor other shaped fiber receiving openings. It is, therefore, intendedthat the foregoing description be regarded as illustrative rather thanlimiting, and that the scope of the invention is given by the appendedclaims together with their full range of equivalents.

What is claimed is:
 1. A method of making a multi fiber ferrulecomprising the steps of: providing a ferrule blank having a pair ofpreformed slots extending inward from opposing sides toward a fiberreceiving cavity which extends from a mating face to a rear end;precisely aligning the blank on a mandrel placed within the fiberreceiving cavity; broaching a pin slot in each side surface such thatthe pin slot is precisely located with respect to the fiber receivingcavity to form a ferrule main body; positioning the ferrule main bodywithin a ferrule receiving opening of a central fixture such thatlocating pins of the central fixture are positioned within the pinslots; populating the fiber receiving cavity with a plurality of opticalfibers; accurately positioning the optical fibers using a plurality ofcombs over ends of the optical fibers which protrude from the matingface; and, filling the fiber receiving cavity with an encapsulant. 2.The method of claim 1 wherein a first pair of combs is slid over themating face to accurately position the plurality of fibers between teethof the combs in a fiber receiving area of the combs.
 3. The method ofclaim 2 wherein a second set of combs is slid over the first set ofcombs and through protruding ends of the optical fibers in a directiongenerally orthogonal to the first set of combs.
 4. The method of claim 3wherein the second set of combs is positioned such that referencesurfaces of the second set of combs engage the locating pins toappropriately position the protruding fiber ends with respect to thepins.
 5. An assembly tool for assembling a multi fiber array ferrulecomprising: a table having a central opening passing between first andsecond major surfaces; a plurality of guide slots formed on the firstmajor surface extending between an edge of the table and the centralopening; a plurality of comb mounts resting upon the first major surfaceof the table and slidingly fitting within one of the guide slots; a combbeing mounted to each respective comb mount; and, a central fixturebeing mounted on the first major surface adjacent to the guide slots andover the central opening, the central fixture having a ferrule receivingopening passing therethrough and in communication with the centralopening and at least one locating pin mounted within the ferrulereceiving opening.
 6. The assembly tool of claim 5 further comprising acomb holder being mounted to a respective comb mount to receiving eachcomb.
 7. The assembly tool of claim 5 wherein the combs are mounted toslide along a top surface of the central fixture.
 8. The assembly toolof claim 7 wherein at least one of the combs further comprises areference surface for engaging the at least one pin.
 9. The assemblytool of claim 8 wherein each comb includes a plurality of interlockingteeth forming spaces therebetween for receiving fiber ends.
 10. Theassembly tool of claim 9 wherein the combs are moved into an engagementposition by sliding the comb mounts within the guide slots.
 11. Theassembly tool of claim 10 further comprising an encapsulant supply tubepassing through an opening in a ferrule main body and being insertableinto the ferrule receiving opening.